Method and apparatus for metallic impregnation of carbon and graphite



Aug. 6, 1968 R. REMION 3,396,054

METHOD AND APPARAT FOR METALLIC IMPREGNATION OF CARBON AND GRAPHITEFiled March 13, 1964 2 Sheets-Sheet 1 1 V4// i I 11 lnvenlor y Mm! Aug.6, 1968 R. GREMION 3,396,054

METHOD AND APPARATUS FOR METALLIC IMPREGNATION OF CARBON AND GRAPHITEFiled March 13. 1964 2 Sheets-Sheet 2 Fig.2 Fig.3

4a 7 4a /A 7 7 Fig.6

9 Claims. (61. 117-227 ABSTRACT OF THE DISCLOSURE Carbon or graphitematerial is impregnated with a metal by surrounding it and the metal insolid form by powdered natural graphite. The latter is sufficientlyfluid or deformable to transmit the pressure and sufficientlyimpermeable to prevent the melted impregnating metal from penetratingthrough it when subjected to a pressure of 150 to 200 kg./cm. and heatedby direct release of heat within the carbon or graphite material and themetal.

The present invention relates to processes for metallic impregnation, toapparatus therefor, and to members impregnated thereby.

The impregnation of graphite -by means of molten metals such as copper,silver or lead is generally effected in an autoclave. After evacuationof the autoclave wherein the members to be impregnated are located incontact with the molten metal, a gaseous pressure may then be applied inorder to aid impregnation. These operations using vacuum and pressurealternately may be repeated.

The present invention has for an object a new process for impregnationwhich does not necessitate the use of an autoclave and a gaseouspressure, While ensuring an equivalent rate of impregnation.

The invention consists in a process for impregnating carbon or graphitewith a metal, in which the carbon or graphite and the metal in solidform are surrounded by an electrically conductive material which issubstantially impermeable to the metal when molten and subjected to apressure of from 150 to 200 kg./cm. a pressure of from 150 to 200'kg./cm. is applied to compress said material, and the carbon orgraphite, the metal and the electrically conductive material are heatedby direct heating to a least the melting point of the metal.

In order that the invention may be more clearly understood, referencewill now be made to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic longitudinal section of apparatus forcarrying out the process of the invention,

FIGURES 2 to 5 are diagrammatic longitudinal sections on a smaller scaleillustrating the successive operations of assembling the apparatus shownin FIGURE 1; and

FIGURE -6 is a diagrammatic longitudinal section of another embodimentof apparatus for carrying out the process of the invention.

In a graphite matrix 1 is located the member (or members) 2 of carbon orgraphite to be impregnated and the metal 3 which it is desired to causeto penetrate into the graphite. The matrix 1 has a base-plate 7 whichcan subsequently serve as a mould-ejector.

The assembly of the member 2 and impregnating metal 3 is surrounded by apacking of compressed natural graphite 4a and 4b. At the two ends of thepacking are located graphite pressure members 6 each in direct contactwith a copper electrode 8.

The upper and lower electrodes 8 are connected with nited States Patenta source of electrical current schematically indicated at 14 by aflexible braided conductor 9 and a rigid conductor 1% respectively.Heating is effected in such a manner that the impregnating metal 3 ismelted, and mechanical pressure is applied by means of a graphite piston5 fitting in the matrix 1 and a screw-jack 12, the pressure beingtransmitted by the pressure members 6 and by the natural graphite 4a and4b. The packing comprises a natural graphite powder, of suitable grainsize, for example from 10 to microns, and is sufiiciently fluid totransmit the pressure and sufiiciently impermeable to preevnt the meltedimpregnating metal from penetrating through it when subjected to apressure of from to 200 kg./cm.

The screw-jack 12 is mounted in a strong metal stirrupshaped frame 13,and the whole assembly of the graphite matrix 1 and its contents, thepressure members 6 and the electrodes 8 is insulated from the screw-jack12 and the frame 13 by means of Bakelite plates 11.

The following nonlimiting examples describe embodiments of theinvention, in particular impregnation with copper and sliver.

Example I .-Impregnnti0n with copper In a graphite matrix 1 (-FIGURE 2)having a natural graphite base-plate 7, is prepared a packing of naturalgraphite 4a compressed at 200 kg./cm. A cavity is made, e.g., bymachining, in the packing 4a (see FIG- URE 3) in which is located themember 2 to be impregnated and a quantity of copper 3 (see FIG- URE 4).The Whole is covered with natural graphite 4b compressed at 150 l g./cm.(see FIGURE 5). The metal 3 may be in any suitable form. for examplepowder or grains. To the piston 5 and the base-plate '7 are applied thepressure members 6 and the electrodes 8 (FIGURE 1), which electrodes maybe, for example, of copper, and heating is effected by means of thedirect Joule effect, maintaining the pressure applied below 150 kg./cm.When the temperature at the core of the packing is at least 1083 C.,i.e., the melting point of copper, pressure is progressively increasedto reach 200 kg./cm.

Cooling is effected while maintaining pressure for several minutes. Theimpregnated members, having a porosity of 10%, are found to contain upto 30% of copper, this quantity being established by the ratio:

weight of copper Weight of the member after impregnation It has beenfound that the ratio of impregnation is equal to that of membersimpregnated in an autoclave under a gas pressure of 50 kg./cm.

Example ll.lmpregnation with silver The same method is followed withsilver as with copper. The results obtained are comparable and evenbetter, since the amount of silver which penetrates into the carbon orgraphite members may be as high as 35%.

Several variations may be effected in the process without exceeding thescope of the invention. It is thus possible to replace the graphitematrix by a metal matrix, protecting it by a refractory and insulatingbody such as carbon black, or preferably by magnesium oxide. FIG- URE 6diagrammatically represents an embodiment in which a metal matrix 1 isinternally coated with magnesium oxide 1a or with carbon black.

In the same way the direct heating may be obtained by means other thanthe Joule effect, thus high frequency heating may be used.

The pressure may be applied by means other than a screw-jack, forexample by a hydraulic jack.

The materials impregnated by the process of the invention, comprisescarbon or graphite impregnated with molten metal, have numerousapplications as regards friction materials, materials for brushes,electrical traction shoes, collectors, electrical connectors andmaterials used in the field of chemistry and nuclear energy.

I claim:

1. In a process for impregnating a substance selected from the groupconsisting of carbon and graphite with a metal selected from the groupconsisting of copper and silver, the steps of surrounding said substanceand said metal in solid form by a powdered natural graphite which issubstantially impermeable to said metal when molten and subjected to apressure of from 150 to 200 kg./cm. applying a pressure of from 150 to200 kg./ cm. to compress said powdered natural graphite, and heatingsaid substance, said metal and said powdered natural graphite byinternal generation of heat therein to raise the temperature to at leastthe melting point of said metal.

2. In a process according to claim 1, the steps of applying electrodesto pressure members in contact with said powdered natural graphite, andeffecting said internal generation of heat by the Joule effect.

3. In a process according to claim 1, the step of effecting saidinternal generation of heat by high frequency heating.

4. A process according to claim 1, wherein said powdered graphite isfrom 10 to 75 microns in grain size and acts as a fluidpressure-transmitting medium.

5. A process according to claim 1, wherein said pressure and temperatureare sufficient to cause 30% to 35% by weight of said metal to penetratesaid substance.

-6. Apparatus for impregnating a substance selected from the groupconsisting of carbon and graphite with a metal selected from the groupconsisting of copper and silver, comprising a matrix of refractorymaterial, arranged to surround a packing of powdered natural graphiteenclosing said substance and said metal, said packing beingsubstantially impermeable to said metal when molten and subjected to apressure of from 150 to 200 kg./cm. means for applying a pressure offrom 150 to 200 kg./cm. to said packing, and means for heating saidsubstance, said metal and said packing by internal generation of heattherein to raise the temperature to at least the melting point of saidmetal.

7. Apparatus according to claim 6, wherein said matrix is of metal witha refractory and insulatory lining selected from the group consisting ofmagnesium oxide and carbon black.

8. Apparatus according to claim 7, wherein said lining is of magnesiumoxide.

9. Apparatus according to claim 7, wherein said lining is of carbonblack.

References Cited UNITED STATES PATENTS 1,088,734 3/1914 Schroers 1172272,255,120 9/1941 Kiefer et a1. ll7227 X 2,847,332 8/1-958 Ramadanofill7228 2,898,243 8/1959 Wenden ll7229 X 2,934,460 4/1960 Ramandanoff1l7-228 3,294,572 12/1966 Piccione et a1. l17228 X ALFRED L. LEAVITT,Primary Examiner.

J. -R. BATTEN, 1a., Assistant Examiner.

